According to the prior art, for instance in case of so-called manhole liners, tube elements made of fiber cement are provided, which keep clear a through-opening in a wall or floor element after casting in concrete. Therethrough, a line can be fed subsequently and can be sealed against the tube element. Further developments relate to a substitution of the tube elements made of fiber cement by tube elements made of metal or also a synthetic material.
The problem the present invention is to solve is to provide a duct having improved use properties.